Having superior performance in mechanical properties, electrical properties, thermal properties, chemical resistance, adhesivity, etc. when cured, epoxy resins are used in a wide range of applications including paints, electrical and electronic insulators, adhesives, etc.
Also, owing to superior physical properties such as hardening strength, hardness, sunlight resistance, processability, etc. and lack of the risk of evaporation of volatile substances or shrinkage during curing, epoxy resins are often used in paints coated on concrete materials after being mixed with suitable curing agents. When compared with other types of paints used for concrete protection, epoxy-cured paints are suitable because of less shrinkage and high mechanical and chemical resistance.
Meanwhile, nonylphenols are used in various industrial applications, including curing agents or plasticizing agents for epoxy-cured paints, owing to their intrinsic physical and chemical properties. However, as nonylphenol is known to induce renal toxicity and disrupt endocrine hormones, its industrial use is gradually prohibited or restricted. Especially in Europe, use of nonylphenol is prohibited entirely or restricted not to exceed 0.1% in products in some applications since 2003. EU Directive 2003/53/EC and EU REACH also regulate and control nonylphenols in the same way [Annex 17, REACH]. Also in Korea, use of nonylphenol is prohibited entirely in some products since January, 2010.
However, the related industries find difficulties due to the lack of materials that can replace nonylphenol. To replace nonylphenol, physical and chemical properties equivalent or comparable to those of nonylphenol are necessary.
Inspired by the fact that the viscosity and hardening properties of styrenated phenol are similar to those of nonylphenol, the inventors of the present invention investigated the possibility of use of styrenated phenol as an alternative to nonylphenol as a curing agent or a plasticizing agent for an epoxy resin.
Styrenated phenol is prepared from alkylation of phenol with styrene. Styrenated phenols may exist as monostyrenated phenol (MSP) having one styrene bonded to the benzene ring of phenol, distyrenated phenol (DSP) having two styrenes bonded and tristyrenated phenol (TSP) having three styrenes bonded. Although the styrenated phenols are commonly used as antioxidants for synthetic rubbers or resins, use of styrenated phenol as a curing agent or a plasticizing agent for an epoxy resin has not been reported yet.